Voltammetric analysis of weak acids with microelectrodes

The role of H+ on the steady-state voltammetric limiting current (I-L) of weak acid (HA) reduction was studied considering results from either lactic acid or acetic acid solutions at constant pH. For solutions with pH > pK(a) or pH congruent to pKa the [H+] effect on the I-L vs c(HA) slope was important even when the H+ current contribution was minor. In contrast, when the pH < pK(a) high H+ current contributions were found; nevertheless the I-L VS c(HA) slope was almost insensitive to pH. A general relationship between I-L and c(HA) was derived considering both the H+ current contribution and the dissociation extent. This equation allows the analytical determination of weak acids, alone or in the presence of strong acids, from experimental I-L and pH. Acid identification can also be performed through the expression presented, following the I-L susceptibility to pH at constant c(HA). (C) 2004 Elsevier B.V. All rights reserved.